Wikipedia claims that Nashville has passed Memphis as of 2016 Census estimates, but I couldn't find confirmation of that in a primary source. They're certainly close. If someone can point me to the raw data, I'll update the quiz.
Google isn't a primary source. It's hard to determine exact numbers when "city proper" isn't a universal term. Nevertheless, I found the following from the Census Bureau 2016 Estimates:
Nashville-Davidson metropolitan government (balance): 660k
Memphis city: 652k
The 2015 estimates were essentially equal, but it does seem like Nashville has recently come out on top, so I've updated the quiz.
Looks like Charleston passed Columbia by about 10k in the 2020 census. I've updated the quiz, thanks. I imagine there are a few others that may need to be checked.
Nashville-Davidson metropolitan government (balance): 660k
Memphis city: 652k
The 2015 estimates were essentially equal, but it does seem like Nashville has recently come out on top, so I've updated the quiz.